1. Field of the Invention
The present invention relates to a traction control device for a vehicle.
2. Description of the Related Art
In a known engine, when the engine is accelerated, slippage of the driven wheel is detected by determining the difference between the speed of rotation of the free running wheel and the speed of rotation of the driven wheel, and when slippage of the driven wheel occurs, the output torque of the engine is reduced by stopping the supply of fuel fed into some of the engine cylinders (see Japanese Unexamined Patent Publication No. 58-8436). In this engine, the number of engine cylinders to which the supply of fuel is stopped is increased as the slippage becomes greater, and thus the output torque of the engine is controlled in accordance with the amount of slippage.
Nevertheless, when the temperature of the engine is low, since the temperature of the interior of the intake manifold is also low, the fuel injected by the fuel injectors cannot be easily vaporized, and thus a part of the fuel is temporarily accumulated on the inner wall of the intake manifold. Consequently, at this time, even if the supply of fuel to some of the engine cylinders is stopped, the fuel accumulating on the inner wall of the intake manifold seeps into some of the engine cylinders. At this time, however, the fuel fed into some of the engine cylinders cannot be burned or, even if the fuel is burned, a good combustion cannot be obtained, and consequently, a large amount of unburned HC is discharged into the exhaust passage. In addition, when the temperature of the engine is low, the amount of fuel injected by the fuel injectors is normally increased, and consequently, a large amount of unburned HC is discharged from the remaining engine cylinders to which the supply of fuel is not stopped. Therefore, when the temperature of the engine is low, if the supply of fuel for some of the engine cylinders is stopped, a large amount of unburned HC is discharged into the engine cylinders. Furthermore, if the supply of fuel for some of the engine cylinders is stopped, a large amount of oxygen is discharged into the exhaust passage from some of the engine cylinders. Consequently, since a large amount of unburned HC is burned in the exhaust passage, a problem occurs in that parts of the exhaust system, for example, the catalyst, are damaged due to the heat radiated during the burning of the unburned HC.
In addition, as mentioned above, even if the supply of fuel for some of the engine cylinders is stopped, since the fuel accumulating on the inner wall of the engine cylinders seeps into some of the engine cylinders, the fuel can be burned in some of the engine cylinders. At this time, however, since the amount of fuel fed into some of the engine cylinders is small, the burning time becomes long. Consequently, when the intake valve is opened, the burning gas flows back into the intake manifold, and thus a problem occurs in that the fuel adhering to the inner wall of the intake manifold is burned, i.e., a backfire occurs.
In another known engine, when slippage occurs at the driven wheel, the output torque of the engine is reduced by retarding the ignition timing (see Japanese Examined Patent Publication No. 53-30877), but a reduction in the output torque by retarding the ignition timing is limited, and thus a satisfactory traction control cannot be obtained.